Unearthly

From Seven Seas:

Ann was once shy and withdrawn until her crush on pretty boy Jem makes her take notice of the world around her. But her blossoming love life hits a snag when Jem attracts the attentions of Rae, the most beautiful girl in school.

Sure, it might seem like your average high school love triangle... until an identity-snatching alien from outer space jumps into the fray and things go helter-skelter!